Suggestions for paper-mulch trials

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CIRCULAR No. 77

UNITED STATES DEPARTMENT OF AGRICULTURE
WASHINGTON,D.C. j

MAY, 1929

RECEIVES

SUGGESTIONS FOR PAPER-MULGH TRIALS on.

By L. H. Fuint, Associate Physiologist, Biophysi 4 Laboratory, Bw “eas, of
Plant Industry U. 8, Bepestmert of Avriculomre

CONTENTS
Page Page
ANGLO GR GELOMI A een a er nas Rees Eee 1 Application of mulching paper—Con
Soil conditions in relation to paper MethodS 2225. tae ee ae 4
Pe THO ne eee ee es Ses re eee 3 Costs = 252 Ss ee EG Ee 4
Application of mulching paper______ 4 General precautions_—-—~—___=-_-2= ns
PUD CES: © Setsmmert te) res b Ss Me 4

INTRODUCTION

The use of paper mulch in agriculture was originated in 1914 by
CG. F. Eckart in connection with the culture of suugar-cane in the
Hawaiian Islands. Following a period of experimental triai the
process was extended to pineapple culture and in 1922 attained
appreciable economic importance in that industry. This method
consists essentiaily of extending black paper over “soil surfaces ad-
jacent to crop plants, the paper serving to enhance growth chiefly
through the suppression of weeds and through the increase of soil
temperature and moisture.

In 1924 the United States Department of Agriculture began small
trials with various types of paper mulches. These experiments, were
continued over a period of four years, during which various phases
of the process received attention. The trials were reported in Tech-
nical Bulletin No. 75.1. For the most part “ie paper used in these
trials proved durable through several seasons and was of the type
used extensively in the pineapple-growing industr y of the Hawaiian
Islands. These trials led to the conclusion that under a wide variety
of crops and conditions a definite and appreciable plant stimulation
resulted from the use of the paper. This conclusion has been sub-
stantiated by further experiments and by the results of a large nuim-
ber of trials. by interested growers throughout the Un ited States
and Canada during the past season (1928).

Little is known, however, concerning the economic value of the
process. The trials in 1928 were made with various types of paper
of varying cost and durability. In most of these experiments there
was no attempt to investigate the relations of the cost of the paper
to the soil surface covered or to the di urability of the paper, or the
relations of the durability of the paper to the requirements of the

1FLIN?, L. H. CROP-PLANT STIMULATION WITH PAPER MULCH, -U. S. Dept. Agr. Teciu.
Bul, 75, 20 p., illus. 1928.

46330°—29 ft

2, CIRCULAR 77, U. S. DEPARTMENT OF AGRICULTURE

crop for which it was used. In many instances papers of a dura-
bility of several years, and proportionately expensive, were applied
to crops maturing in a few months. No particular attention had
been given to the development of methods for the adaptation of
mulching paper to the growing of any one crop. ‘The rather pro-
nounced increases in growth reported from the use of paper had led
enthusiasts to plan the covering of large areas; but without experi-
mental evidence that the method was adapted to the local conditions
_and that the type cf paper was satisfactory such a procedure would
undoubtedly have resulted in many disappointments. On this ac-
count it has been the policy of the department to suggest that all
‘initial trials be conducted on a small scale.

With the establishment of the fact of crop response for a variety
of crops, soils, and seasons, the further study of paper mulch be-
comes of interest. Hrom a technical viewpoint this study is associ-
ated on the one hand with types of papers and their suitability for
different crops and on the other hand with the biophysical factors
involved in crop production under the paper-mulch system. This
technical study is being carried out by means of experiments at
the Arlington Experiment Farm (Rosslyn, Va.) and elsewhere,
but these experiments must be repeated throughout several seasons
under varying conditions of soil, season, and climate before definite
conclusions can be reached. : |

From an immediately practical standpoit the further study of
paper mulch involves additional and extended field trials in the
producing regions. The paper-mulch method is a new one in con-
tinental United States, and its economic utilization here is still in
the experimental stage. Because the method is a new one there
has been no thorough testing of available mulching papers and
no studied development of methods for their adaptation to our
crops. Those who have been fortunate in the selection of their
papers and ingenious in applying them appear to have attained an
appreciable and encouraging measure of success. Others who did
not apply the paper until the season was well advanced, or who
found that their paper had blown away or had disintegrated or
had been interfered with in some other way, obtained results that
were not indicative of the effectiveness of the paper. Whether the
“best paper” for any crop and the “best method” of using it will
make the method economic for use with a certain crep in a certain
region is not a matter that can be determined without practical experi-
ment and repeated trials in that particular region. The economy
of the practice is particularly related to labor costs, to the type of
crop, and to specific market conditions, and is therefore essentially
a matter for the interested grower to determine for himself, with
the experience of others to guide him. The solution of the problem
requires initiative, resourcefulness, and hard work, but its solution
‘appears to offer satisfactory rewards. |

The wide interest in paper mulch indicates that the method will
be given a thorough trial in this country. The experienced grower
will recognize that the determination of the potential value of a
system of culture so radical as the paper-mulching system, for any
specific agricultural purpose, is pioneering work. Utilizing the
system to economic advantage in continental United States will un-

= SUGGESTIONS FOR PAPER-MULCH TRIALS 3

doubtedly require the same research, resourcefulness, and industry
that brought about its successful development in the Hawaiian Is-
lands. Present paper costs are deemed to limit the application of
the system in this country toe the more intensive phases of our agricul-
ture, but for these it appears to merit serious study.

The present circular is intended as a guide to growers interested
in the practical possibilities of paper mulch, who are desirous of
ascertaining through small trials whether or not they may make
economic use of the stimulation of plant growth and other advantages
which frequently result frem the application of paper mulch.

SOIL CONDITIONS IN RELATION TO PAPER MULCH

The trials with paper mulch have not as yet indicated the desir-

ability of any one particular method of soil preparation for general
use. It is quite possible that on account of the modified soil condi-
tions accompanying the use of paper mulch the present practices in
relation to certain crops on unmulched soils may undergo some
change. Nevertheless, such changes may be expected to develop
gradually with further practical experience. For example, soil-
moisture conditions produced under the mulch may be of such im-
portance where irrigation or dry-land agriculture are practiced, or
in regions of excessive rainfall, that a modification of present technic
may “be practicable and advisable. Or, again, the effectiveness of
the paper in bringing about the rapid decomposition of weeds may
possibly be utilized in the development of a modified system of green
manuring. Further, the protection afforded by the use of certain
types of paper against the packing of heavy soils by winter rains
and snows may p yermit advantageous fall preparation of the soil for
early spring planting of certain crops. On soils described as “ cool
and moist,” however, the special desirability of applying the paper
over slightly ridged beds has been shown to be due to the fact that
under these conditions the soil temperature was increased through
the reduction of evaporation and through heat absorption. Ai the
same time the soil moisture was not unfavor ably increased, as some-
times happened on such soils with paper and flat culture.

Little is known regarding the relation between the use of paper
muich and the application “of fertilizers. The initial paper-mulch
trials have indicated that the poorer the soil the greater the percent-
age difference between the mulehed and the unmuiched crop. Even
with a relatively great increase in yield resulting from the mulch the
yield might still “be unprofitable. The absolute difference between
mulched and unmulched crops increased with fertility. It is deemed
entirely reasonabie to look to the paper mulch for an increase in
soil moisture and soil temperature. In so far as these factors ma ay
promote growth directly, well and good; but their indicated s
ondary effect in promoting the activity of favorable microor ganisms
in the soil, leading to an need production of nitrates, can take

(9 place only through the same reduction of the organic materiais in
the soil which characterizes all the usual practices. The introduc-
tion of paper mulch into the pineapple-growing industry did not
result in a reduction of the applications of manures or commercial
fertilizers, but it did enhance the effectiveness of any added fertility.

4 CIRCULAR 77, U. S. DEPARTMENT OF AGRICULTURE

Pending further investigation, the validity of this relationship may
well be assumed in the use of paper mulch with crops in temperate
climates.

APPLICATION OF MULCHING PAPER

PAPERS

There are at present two general types of mulching papers used
during the growing season. These types are based on durability.
Papers made for use with a single crop are designated as type A,
while those made for use with two or more crops or for home gar-
dens are designated as type B.

The type-A papers comprise those suitable for annual crops in
field culture. They are designed to last as long as or somewhat
less than the period during which the crop plants are in the field.

The type-B papers comprise the papers suitable for perennial
crops in field culture, for a succession of annual crops in field cul-
ture, and for all home-garden purposes. They are appreciably
stronger and more durable than the type-A papers. The paper that
is used in pineapple culture is of type B.

METHODS

There are at present three principal methods of applying paper:
(1) The placing of small squares of paper at regular distances, (2)
the use of extended strips of paper with alternate uncovered soil
areas of approxi-
mately the same
extent, and (3) the
use of paper in
strips without any
uncovered soil ex-
cept that exposed
FIGURE 1.—Method of applying small squares of paper mulch incidental BOs b .

as used with certain vine crops in field culture ’ establishment of the
: = crop plants.

In the first method as apphed to the growing of such crops as.
muskmelons, watermelons, cucumbers, squashes, etc., sections 3 by 3
feet were cut. from 36-inch rolls of type-A paper. Holes of suitable
_Size to permit field seeding or transplanting were then cut in the
- center, and the sections then were placed in the field. The seeds were
planted just before the paper was placed over the prepared seed bed,
or at any subsequent time. The best results were obtained, however,
when the application of the paper was made before the seeds germi-
nated. ‘Transplanting into the field before the laying of the paper
gave better results than transplanting through holes in the paper, as
in the latter case it was difficult to firm the soil about the plants.
The mulch-paper sections were made to’ hold “hot caps” in place
when these were used. The type-A papers used in the above manner
should be about disintegrated at the time of harvest. If they still
remain intact, it indicates that a less durable and less expensive paper
might be as effective. This method is outlined in Figure 1.

in the first method, as applied to the establishment of fruit and
nut orchards, vineyards, shade and forest trees, etc., sections 3 by 3
feet were cut from 36-inch roils of type-B paper. Cross-shaped slits

, SUGGESTIONS FOR PAPER-MULCH TRIALS 5
° 4

of suitable size were made in the center for single-stalk plants, and
round holes with a slit to the outside were made for those with bushy
tops. These sections were placed about the plants at the time they
were set out in the permanent field planting, all outer edges being
depressed and embedded in soil to insure protection against wind
damage. For larger plants two sections 3 by 6 feet were cut from
36-inch rolls of type-B paper, each section was notched at the center
of one long edge, and the two were overlapped slightly about the
plant stock. All outer edges were covered with sou, and bricks,
stones, or sods were placed on the overlaps. The type-B papers as
above used were left in place until disintegration had destroyed their
effectiveness.

The particular desirability of a single application of paper lasting
several years as compared with an annual application of paper last-
ing for the growing season only is-complicated at present by the lack
of information regarding the influence of paper mulch during the
winter season. The application of paper to well-developed orchard
trees did not appear to be of genera] economic promise.

In the second

method, as apphed ee ad ae
to the growing of ee ee oe

fs Sng Ro VY ee eens
such crops as =. 7" eee
tomatoes, peppers, == Pee

] NS v ae

eggplant, cabbage, od eee
and tobacco, the Nee

type-A paper 36: ie
inch id FicguRE 2.—Method of applying extended strips of paper
inenes wide Was ruich, as used with various crops in field culture

unrolled over pre-
pared soil, and the edges covered with soil. The paper-covered area
was slightly ridged so that the heat-absorbing value of the paper
would not be reduced by any deposition of soil on top of the paper
-by subsequent rains. This method with type-B paper is the one used
with pineapples, and the machine laying of the paper in such a way
does not involve any mechanical difficulty. The young plants were
set through cross-shaped slits, or in some instances suitable-sized
disks of paper were removed. Double staggered rows of plants were
set through at the desired intervals. The openings made for the
plants also facilitated the entrance of rain water. The machine
preparation of the slits may be readily accomplished at the factory
if continued trials indicate the desirability of extensive application.
With this method the middles required machine weeding. I¢ is quite
possible that if wider papers were available more than two rows of
plants could be grown to greater advantage. For the present, how-
ever, the double-row system appears best for trials of the above-listed
erops when hand set in the field. This method is shown in Figure 2.

With strawberries a similar system was used, a type-A paper be-
ing used in the Southern States, where this plant is grown as an
ge and 2 type-B paper being used elsewhere. Since the paper

nds to prevent the establishment of runner plants, all plants de-
sired were set out when the bed was made.

In the second method, as applied to the growing of such crops as
sweet corn, potatoes, sweet potatoes, cabbage, and tobacco, when the
eventual adaptation of the system to machine planting was projected

) CIRCULAR 77, U. S. DEPARTMENT OF AGRICULTURE

the use of type-A paper in 18-inch widths was used. The paper
was laid over slightly ridged rows and held with soil over the de-
pressed edges. Suitable provision for transplants or for plant
emergence was-made by splitting or cutting out disks at the desired
intervals—a somewhat laborious process at present but one which
can readily be handled at the paper mills if trials appear to warrant
it. It is quite possible, moreover, that the machine laying of such
prepared paper may be synchronized with the pianting.

In the third method, as applied to the growing of drilled crops in
field culture, accurately spaced machine seeding has been immediately
followed by the iaying of strips of type-A paper held with staples,
stapled laths, or edgings. Protection against wind damage was hard
to secure with this method and type-A papers, and it constituted the
most difficult problem in the use of paper mulch with drilled crops.
A further problem was that of hand weeding within the row without
destroying the paper. This method is shown in Figure 3.

The above method
was also used in the
culture of celery,
following accu-
rately spaced field
planting, and for
various flowering
plants grown for
bulb or cut-flower
production.

Figur» 3.—Method of applying strips of paper mulch in In the th ir d
block formation, as used with drilled crops in field cul- : :
ture and in home gardens method, as applied

to the growing of
young evergreens, boxwood, and various types of perennial nursery
stock, the laying of strips of type-B paper followed the lining out of
the plants at suitably spaced intervals. The paper was held with
wire staples, stapled laths, or edgings.

A modification of the third method, as apphed to the growing of
nursery stock, consisted in the use of a strip of paper with notches
2 inches deep cut along one side at the desired intervals. Following
the laying of one strip of this paper the plants were set within
these notches, and the soil was leveled. The second strip of paper was
then overlapped with the straight edge touching the plant stalks and
held with stapled laths. Three holes were made in each lath, one
near each end and one in the center, and through these holes were
inserted straight wire pegs of No. 10 wire, 10 inches long and pro-
vided with a double bend at the top to hold the lath. This method
proved very effective protection against wind damage except under
conditions of pronounced soil heaving with frost, and had the ad-
vantage of a practically complete weed suppression.

fn home gardens all three of the above methods were used with
both the A and B types of paper. The type-B paper was clearl
indicated as much more desirable for ali home-garden purposes.
for ornamental home plantings the paper was covered with pine
straw to efface the somewhat unsightly appearance of the black paper.

“J

7 SUGGESTIONS FOR PAPER-MULCH TRIALS

COSTS

Although most of the mulching paper used in the Hawaiian
Islands is manufactured in the United States, the delivered cost in
quantity for consumption there is nevertheless appreciably below the
present cost of comparable paper in this country. During the past
season, however, a number of companies have devoted much effort to
the quantity production of mulching papers, and it is probable that
with increasing numbers of types of paper and enlarged use, the
present costs of papers suitable for various mulching purposes may
be gradually reduced. The present cost of the paper-mulching system
depends upon the type of paper used and the method of use. With
an inexpensive type-A paper costing $1 per 500 square feet the cost
of the paper required for 3 by 8 foot squares spaced at 12-foot
intervals would be about $5.50 to the acre of 302 squares. This
minimum expense involves the use of an inexpensive paper, but it
will readily be seen that the use of squares of more durable and
expensive paper in the establishment cf orchards does not appear
prohibitive. The cost of the type-B papers varies from two to three
or more times the cost of the type-A papers. As used in the produc-
tion of many annual crops in field culture with the system of extended

-cropped and mulched rows with uncovered interspaces, the type-A
papers, in quantity, have an approximate minimum cost of about
$30 per acre. As used in the practically complete covering of the
soil the type-A papers have an approximate minimum cost, in quan-
tity, of about $60 per acre, while the more durable type-B papers,
similarly used, will cost $120 to $200 per acre, the cost being distribut-
able against use for two or more crops or seasons.

The cost of applying the paper depends upon the method of use,
but ordinarily it appears to be only a small percentage of the cost
of the paper.

On the basis of present costs, the use of paper mulch is not profit-
able in the ordinary production of such crops as field corn, dry beans,
cotton, sugar-cane, and other low-value crops. The paper is effective
with these crops, however, and it is entirely possible that, should the
manufacture of mulching paper from waste by-products (e. g.,
pressed cane, cornstalks, etc.) prove feasible, its application to low-
value crops might become a matter of practical interest.

GENERAL PRECAUTIONS

In making small-scale trials with paper mulch the system was con-
sidered as experimental, and provision was made for suitable com-
parison areas without paper. The papered areas were as nearly as
possible of the same fertility as the comparison areas which were not
papered. The preparation of the soil and the planting were done at
the same time on both areas, and any fertilizer subsequently applied

_ was applied equally to the mulched and unmulched areas. Under iuri-
) eo conditions special precautions were taken to prevent excessive
oisture under the paper, and on moist soils the paper was extended

over ridged and shghtly elevated beds to facilitate drainage.

In conducting the initial trials the main objective was the determi-
nation of the extent of crop-plant stimulation attributable to the use

Ss pe (7, U. S. DEPARTMENT OF AGRICULTURE

of a Sho impervious paper. When this was ascertained it consti-
uted a basis for any study of particular papers and methods of
applying them which seemed desirable.

As stated on page 18 of Technical Bulletin No. 75,2 certain methods
of using mulch paper are patented. The present licensees are the
Paraffine Companies (Inc.), of San Francisco, Calif.; Bird & Son -
(Inc.), East Walpole, Mass., and Chicago, Tl. - and The International
Paper Co., 100 East Forty-second Street, New "York, N. Y.. So far as
these investigations show, any impervious dark paper free from
soluble toxic materials may be as efficacious in stimulating plant
growth as that manufactured especially for use as a mulch.

The successful application of paper mulch in other regions has
been brought about only through modest initial trials annually ex-
tended as more information was obtained. ‘There appears to be no
reason why the present inquiry regarding the attractive possibilities
of this system should not be extended i in a » similar manner.

2Frint, Lb. H. Cp. cit.

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